Silica Supported Group IV Metal Complexes Prepared via SOMC for Arene Hydrogenation Reactions

Peijie Hu and Keith Searles

Department of Chemistry, University of Florida

Surface organometallic chemistry (SOMC) is a well-established approach for the controlled preparation of well-defined heterogeneous catalysts. By gaining a molecular-level understanding of heterogeneous catalysts, it becomes possible to identify active sites and establish relationships between structure and activity.  In this study we report the grafting of  homoleptic metals complexes [M(CH₂tBu)₄], (M = Ti, Zr, and Hf), on fumed silica partially dehydroxylated at 700 ^oC yielding the surface sites [(≡SiO)M(CH₂tBu)₃] and [(≡SiO)₂M(CH₂tBu)₂]. These materials are characterized through qualitative IR spectroscopy and quantitative NMR experiments, studying the surface composition and distribution of surface sites. The catalytic performance of these pre-catalysts are investigated under semi-batch reactor conditions for hydrogenating a variety of aromatic substrates under relatively mild temperatures and pressures. Mechanistic considerations will be discussed suggesting active sites different from [(≡SiO)₂ZrH₂] and [(≡SiO)₃ZrH], which have been previously proposed as active catalysts for hydrogenation of unsaturated hydrocarbons.